Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add BrentFarris/echo --skill mobile-viewport-overflowgit clone --depth 1 https://github.com/BrentFarris/echoWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/brentfarris/echo/mobile-viewport-overflow)<a href="https://agentmods.dev/skills/brentfarris/echo/mobile-viewport-overflow"><img src="https://agentmods.dev/badge/skills/brentfarris/echo/mobile-viewport-overflow/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/brentfarris/echo/mobile-viewport-overflow"><img src="https://agentmods.dev/badge/skills/brentfarris/echo/mobile-viewport-overflow.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00038 | $0.00702 |
| Opus 5.5 | $0.00015 | $0.00281 |
| Sonnet 5.5 | $0.00008 | $0.00140 |
| Haiku 4.5 | $0.00004 | $0.00070 |
Grade A, and why
mobile-viewport-overflow scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 31 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Mobile viewport overflow in the Echo SPA
Symptom
On phones the whole page can scroll/pan down and right past the app, which renders smaller than the screen with empty space around it. A stray plugin count badge may float at the screen edge.
Root cause chain
.mobile-nav-tabs(inweb/css/app.css,@media (max-width: 720px)) is the horizontal scroller for the mobile nav tabs. Its content (.tabsScrollW≈ 400-450px) routinely exceeds its width (~222px), so later tabs sit beyond the right edge, clipped.- Any
position: absolutedecoration inside those tabs (e.g..plugin-count, which has notop/leftand relies on static position) resolves its containing block to the nearest positioned ancestor..mobile-nav-tabhad noposition, so the containing block was.mobile-bottom-nav(position: relative) — an ancestor OUTSIDE the.mobile-nav-tabsscroller. Per CSS overflow rules, an abspos element whose containing block is an ancestor of a scroller is NOT clipped by that scroller. - The badge therefore renders past the nav's right edge and widens the document (e.g. 459px vs 360px viewport).
- Mobile Chrome shrink-to-fit then zooms the layout viewport out to the document width (innerWidth becomes 459), so the app lays out at 360px inside a 459px viewport: pannable empty space right/bottom, everything looking "smaller than the screen".
Rule
Any absolutely-positioned badge/pin inside a scroll-clipped container must have its nearest positioned ancestor INSIDE that container. Fixed by adding position: relative to .mobile-nav-tab (app.css mobile block).
The same rule applies to .mobile-nav-pill, .plugin-notice, and any future decorations in .mobile-nav-tabs or other overflow containers.
Debugging technique
Reproduce with an isolated instance (no auth risk to the user's data): build the Go binary (embeds web/dist — run npm run build in web/ FIRST or you verify stale CSS), run it with -port=<free> -data=<temp>/echo.json, drive with Playwright chromium at viewport 360x800, isMobile: true, hasTouch: true, complete setup, create a workspace + stage/approve a builtin plugin (POST /api/plugins/stages {source:{type:"builtin",builtin:"notes"}} then POST /api/plugins/stages/{id}/approve {scope:"global",enable:true}), then evaluate document.documentElement.scrollWidth/scrollHeight vs innerWidth/innerHeight. innerWidth GROWING beyond the viewport width is the shrink-to-fit signature; scan all elements for rects past the viewport to find offenders (skip position: fixed, ignore elements clipped by an ancestor scroller).
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 4d ago First seen · 31 lines · 38 tokens per session scan A e8eecba74cab
mobile-viewport-overflow is a skill published in the GitHub repository BrentFarris/echo (11 stars, last pushed today), licensed MIT. It adds 38 tokens to every session and 702 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-10-12.
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